It is frequently important in modern day technology to precisely position an element at a selected radial location on a rotating platter, disk or similar elements. Some applications which require this sort of positioning are in the entertainment industry and include record turntables, compact disk players and video disk players. Each of these applications utilizes a head which moves on a single continuous spiral track. Various devices such as tracking tone arms and the like have been created to achieve accurate and steady positioning.
The data processing industry utilizes as data storage media a number of devices including rotating disk-like structures having magnetic media coated thereon. These sorts of devices include floppy disks which are packaged in diametrical various sizes ranging from 8.8 cm (31/2 in.) to 13.2 cm (51/4 in.) to 20.1 cm (8 in.) and fixed disks (also known as "hard disks" or "Winchesters") which include rigid rotating disks of various data capacities, stacking numbers and physical sizes. These devices are invaluable for use in the small computer industry as they provide reliable means of data storage and retrieval and rapid techniques for transferring data to and from such storage.
Data is stored on a magnetic media disk on a series of concentric rings formed on the surface of the disk. These rings are known as tracks in floppy terminology or cylinders in Winchester terminology. Each track or cylinder is characterized in that each point on a given track or cylinder has the same radius from the origin or center point of the disk as each other point. The tracks are situated on the disk according to various densities, with one of the most common being 48 tpi (meaning "tracks per inch") radial separation. Depending on the size of the disk and the quality of the magnetic media a different number of tracks may be put on any given disk. The capacity of the disk per data storage is directly dependent upon the number of tracks and the density with which data can be written on those tracks.
Each disk may be dual sided and multiple disks may be present in the same storage device, however, each disk side, during operation, operates within a plane. Therefore the motion and positioning of a given point on the surface of such a disk may be stated in terms of a two dimensional coordinate system. In this instance, it is found that the rotational coordinate system (r=radius and .phi.=angle of rotation) is far superior to the Cartesian system. In the rotational coordinate system each track upon a disk may be described as having a given value for r while any point on that track may be accessed by a given value of .phi.. Conventional usage has established that the tracks are numbered from the most exterior track on the disk to the interior. Therefore for a 60 track disk (in decimal notation), track 0 will be the closest usable track to the perimeter to the disk while track 59 is the closest usable track to the hub of the disk. Typically, only a partial band of the disk surface is actually utilized for data storage. In usage, the disk typically is in continuous rotation and the .phi. component may be determined by reading magnetically coded signals on each of the tracks or by sector defining apertures in the disk itself. The positioning of the read/write head of the apparatus, however, requires moving the head along a given fixed radius for various incremental r values. Ordinarily, the read/write head will move only along a linear track between the origin point of the disk and a fixed (non-rotating) point located outside the disk. In order to accurately read the given tracks on the disk it is necessary to move the read/write head in quantum units or increments with each incremental unit equal to the separation distance of the tracks. For a 48 tpi arrangement the increment between tracks will be 0.052 cm (1/48 in.). It is with this linear incremental positioning that the assembly of the present invention deals.
Various methods have been utilized in the prior art to position the read/write head. These have included lead screws, capstan actuated band drives and other methods of stepper motor actuation. Each of these methods has been successful in positioning the head over the center of the track, with varying degrees of accuracy and speeds of transition.
As with all technology, however, there remains room for improvement in the areas of positioning speed, positioning accuracy, simplicity of operation, reliability, durability, noninterference with other elements within the device, compact size and economy of manufacture. In a highly competitive technology all of the above factors are important targets for improvement, with the latter, economy of manufacture, being perhaps the most important.